From the aforementioned applications and patents and the art and literature cited therein, it is clear that the disposal of radioactive wastes by concentrating them to a maximum possible extent and introducing the radioactive waste into containers which can be sealed, is well known and has long been recognized as a desirable solution to the disposal problem. The containers which can be used are generally thick-wall containers which can be composed, for example, of cast iron, and have walls which are capable of absorbing the radiation emitted by the contents of the container.
In spite of the fact that the art of handling radioactive wastes for such disposal is relatively well developed, problems are still encountered with materials having comparatively weak radioactive or slight radioactive contaminations since such materials are produced in large quantities in nuclear reactor installations and the equipment hitherto required for concentrating such materials is expensive to fabricate, maintain and operate. The problem is especially pronounced in nuclear electricity-generating power plants where evaporator concentrates and solid filter products may have to be disposed of.
Solid wastes of the type with which the present invention is primarily concerned are generally ion-exchange resins which are used in filtering and water-cleaning apparatus in a nuclear power plant, although cellulosic filter materials such as filter tubes, rods and candles also fall into this category. Because all of these solids are able to take up water and are generally recovered from the nuclear power plant impregnated with water and radioactively contaminated to a greater or lesser extent, they have been considered to have a high pore volume and will be referred to hereinafter as water-impregnated bibulous solids.
Another radioactive waste generated in comparatively large quantities in nuclear power plants and requiring disposal is the radioactive or radioactively contaminated evaporator concentrate which has a high radioactive salt concentration but is nevertheless flowable.
In the discussion below, reference will be made to the evacuation of a final storage container for radioactive wastes and to the application of vacuum thereto and for the purposes of this invention the term "vacuum" will be understood to mean a vacuum of sufficient depth to permit vacuum drying or dewatering (see, for example, German patent document DE-OS No. 32 00 331). Such vacuums generally must be generated by vacuum pumps.
We also will refer to final storage containers herein, meaning thereby to indicate the containers in which the radioactive residue is to remain for ultimate disposal, i.e. containers which can be sealed after the process is completed without removal of the radioactive residue therefrom, utilized for transportation of the radioactive waste to the subterranean or other disposal site, and placed at that site for permanent disposal of the residue. Such containers are composed of substances which, like cast iron, can absorb radiation effectively and have a sufficient thickness that they can act, for example, as total neutron absorbers. As the aforementioned patents indicate, the walls of such containers can also be provided with neutron moderator materials or the like.
It may be noted that in the past water-containing solid wastes have been subjected to vacuum drying and, indeed, that evaporator concentrates have been transformed into salts, both radioactive residues being incorporated radioactively in a mass with a binder such as cement, synthetic resin or glass. While these practices have proven to be effective, they are difficult to carry out and expensive, especially since the dried bibulous solids have a very large pore volume so that the volume of the storage container or final disposal container is only partially utilized by reason of the space remaining in the interstices of the bibulous solids.
It is known, for example, to mechanically compact such solids to reduce this wasted volume, but the compaction process is a step which is comparatively costly and may be difficult to carry out at least in some cases.